The present invention is related to that disclosed in U.S. patent application Ser. No. 09/475,604, filed Dec. 30, 1999, entitled xe2x80x9cCOMBINED SYSTEM FOR CALIBRATING RECEIVER GAIN AND MEASURING ANTENNA IMPEDANCE MATCH AND METHOD OF OPERATION.xe2x80x9d U.S. patent application Ser. No. 09/475,604 is commonly assigned to the assignee of the present invention. The disclosure of the related patent application is hereby incorporated by reference in the present application as if fully set forth herein.
The present invention is directed, in general, to wireless communications systems and, more specifically, to a system for measuring receiver antenna impedance match in a base station in a wireless network.
In order to increase the number of subscribers that can be serviced in a single wireless network, frequency reuse is maximized by making individual cell sites smaller and using a greater number of cell sites to cover the same geographical area. Accordingly, the greater number of base transceiver stations increases infrastructure costs. To offset this increased cost, wireless service providers continually implement any improvements that may reduce equipment costs, maintenance and repair costs, and operating costs, or that may increase service quality and reliability, and the number of subscribers that the cellular system can service.
Wireless service providers use a variety of test equipment to monitor the performance of the RF receiver and the RF transmitter of a base transceiver station (BTS). The test equipment may monitor a variety of signal parameters in the RF transmitter, including adjacent channel power ratio (ACPR), spectral purity (including in-band and out-of-band spurious components), occupied bandwidth, RHO, frequency error, and code domain power. The test equipment may also perform a variety of test functions in the RF receiver, including receive antenna impedance matching and receiver calibration. Preferably, the signal parameters are remotely monitored from a central location, so that a wireless service provider can avoid the expense of sending maintenance crews into the field to test each BTS individually. Additionally, a remote monitoring system can detect the failure of an RF transmitter or an RF receiver nearly instantaneously.
Unfortunately, adding some types of test equipment, such as spectrum analyzers, to a BTS significantly increases the cost of the BTS. In some cases, the cost of the test equipment may be greater than the cost of the BTS itself. As a result, wireless service providers frequently do not install test equipment in base transceiver stations, or install only a limited amount of test equipment to test only some of the functions of the BTS. The remaining functions must be monitored by maintenance crews using portable test equipment.
There is therefore a need in the art for inexpensive test equipment that may be implemented as part of the base station. In particular, there is a need for integrated test equipment that can perform reuse some of the existing circuitry in a base transceiver station. More particularly, there is a need for integrated test equipment that can be used to measure the impedance match of the receiver antenna.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a system for determining the impedance match of an antenna for use in an RF transceiver comprising an RF transmit path comprising circuitry capable of amplifying an RF signal and transmitting the amplified RF signal to the antenna coupled to the RF transceiver. In an advantageous embodiment of the present invention, the system comprises: 1) a test signal generator coupled to the RF transmit path and capable of generating a first test signal and injecting the first test signal into the RF transmit path, wherein the RF transmit path amplifies the first test signal; 2) an RF mixer coupled to an output of the RF transmit path and capable of down-converting the amplified first test signal to produce a second test signal at a frequency within a receive frequency band of the RF transceiver; 3) an RF coupler coupled to an output of the RF mixer and capable of transmitting the second test signal into the antenna and capable of receiving a reflection of the second test signal; and 4) a first signal monitor coupled to the RF coupler capable of measuring the reflection of the second test signal.
According to one embodiment of the present invention, the test signal generator generates the first test signal at a center frequency of a transmit frequency band of the RF transceiver.
According to another embodiment of the present invention, the second test signal is at a center frequency of the receive frequency band.
According to still another embodiment of the present invention, the system further comprises a second signal monitor coupled to the RF mixer and capable of determining at least one parameter of the second test signal.
According to yet another embodiment of the present invention, the system further comprises a signal splitter coupled to the RF mixer output capable of generating the second test signal on a first split output and a second split output signal on a second split output, wherein the second split output signal is substantially equal to the second test signal.
According to a further embodiment of the present invention, the second signal monitor monitors the second split output signal to determine the at least one parameter of the second test signal.
According to a yet further embodiment of the present invention, the RF coupler is coupled to, and receives the second test signal from, the second split output of the signal splitter.
According to a still further embodiment of the present invention, the system further comprises a controller capable of comparing at least one parameter of the reflection of the second test signal with the at least one parameter of the second test signal.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.